My experience
I've just gone through this process with my new 7 I built, almost done with Phase I. Here's how I did it. Superior IO-360 with a Whirlwind RV-200 prop. My CHT's were all high all the time, and they would go over 400 even cruising if I brought the power up high. Mind it's summer and hot as **** here in Oklahoma. On a particularly hot day I had to reduce power shortly after takeoff just to keep the front cylinders below 430. During the build a tech counselor advised me to install a washer between #3 and the rear baffle, which left a, well, washer-thickness gap back there.
So, high CHTs most of the time, with #1 and 2 higher than 3 and 4, preventing me from using high power. But I wanted to balance the fuel flows before I did anything with cooling because I wanted to make sure any cooling changes I made were due to airflow issues, not mixture differences. I wasn't exceeding any limits so I wasn't worried about hurting my engine - I just was power-limited. Props to Kyle at Airflow Performance; He spent a lot of time with me on the phone and over email, and long story short, I went from a GAMI spread of 1.8 to 0.1 with Kyle's help. I owe him lunch if I ever meet him. His advice was educational for me. I can cruise LOP smoothly if I want to and my ROP deltas are generally within about 20-30 degrees at most.
So, fuel flow balanced, I started looking at my baffle seals and baffles. I used a scope with the cowl on to see how the seals sat against the inside of the cowl. Found three slight buckles that looked like they might be leaking. Fixed those by adding baffle seal "doublers" to those sections to force the original seal flat against the cowl. No difference in CHTs. The upper seals just behind the prop were a mess. I trimmed and added a doubler to the right side. Still no difference. I retarded the dual p-mag timing 5 degrees (running the B curve). Surprisingly, no difference. Because 1 and 2 were hotter, I trimmed the front air dams down about 3/4" each. Only a very slight difference - the heat "moved" rearward a little. I checked the wrap-around parts of the baffles on the lower forward and rear faces of the fins. The left side had a gap so I tightened up the tensioner to force the wrap-around much closer to the fins. Still no difference. I used high-temp silicon on some leaky areas. Still no noticeable difference.
Finally I looked more closely at the upper front seals behind the prop. Wish I had taken pictures. Maybe I'll post them later if someone wants to see. The very front edges of those seals on both sides, behind the upper inboard sides of the cooling inlets were not pressing tightly against the upper inside contour of the cowl (that I built up with foam and glass. Ramps were installed and sealed per plans at build time). This probably allowed a significant leak. During flight, it's possible that the airflow was causing the front edges of those upper front seals to pry even farther away from the upper contour of the cowl, allowing a much bigger leak. So I came up with a highly technical solution: I installed another rivet on each side of the seal above the forward-most rivets, that caused the seals to hug tightly against the upper inside contour, closing the little triangular opening at the forward edges of the seals. At the same time, I replaced the AN-960 spacer with an L version between #3 and the right rear baffle, halving the gap (I now know about the "hammer relief" method of allowing cooling air by the zero-fin-depth section at the back of Lycoming cylinders, but I haven't done it yet). Also, because 1 and 2 were still warmer than the back, I trimmed the air dams down to approximately half their original height. I did all three of these things before the next flight so I don't know what made the biggest difference.
With all those changes, my CHTs are about 30 degrees lower. I can run max power, best power mixture at 6500 feet and my CHTs are around 370-385 at most on a hot day (today, in fact). TAS 173 knots. Before, I couldn't keep them below 400+ in those conditions. My engine manual says normal operating CHT is 360-385. I'm squarely in that range now at high cruise. At lower power and peak EGT I'm below 360, cruising at 153-ish knots true. I can hold takeoff power now, etc, etc. It's totally fixed my cooling problem and my fuel flows and CHTs are tightly balanced. I'm almost worried that in the winter I'll have trouble keeping the cylinders warm enough at low power. We'll see.
Hope this helps someone.