Hello Todd,
First a clarification. Some postings above are saying that the presence of traffic in the area you are flying will affect the "TIS-B Client %" value being reported in this report from the FAA. This is entirely incorrect.
Whether or not the ground stations are providing you with TIS-B client services is strictly between your aircraft, ATC radar, and the ADS-B ground stations and has nothing to do with having traffic in the area. You must be in radar contact and must be a
valid ADS-B Out aircraft with ADS-B In capability before the ground stations will declare you a TIS-B client and provide TIS-B traffic (Mode C) uplinks.
Notice that this also applies to whether or not you receive ADS-R uplinks, but since you have a GDL39 dual frequency receiver and don't need any help from the ground stations to see ALL ADS-B Out traffic on both 978/1090 Mhz directly (and they know this from your ADS-B Out messages), they don't provide ADS-R uplinks to you.
The meaning "valid ADS-B Out" aircraft has been a moving target. Aircraft transmitting SDA=0 with non FAR 91.227 compliant position sources used to be able to receive TIS-B client services, but early in 2016 the bar was raised to SDA > 0, which made little sense (prior to 2020 which requires SDA=2), but that is what they did. As you know,
FAR 91.227 specifies SDA = 2 (and SIL=3), so raising the bar to provide TIS-B services to aircraft transmitting SDA=1 is only on a temporary condition.
Note that this doesn't have anything to do with you since you are transmitting SDA=3, SIL=3, but we bring this up as history since your SDA=3 is a little unusual. As mentioned above FAR 91.227 doesn't say SDA>= 2, it says SDA = 2.
I just looked at the most recent reports from the two G3X EAB aircraft we fly, and both are transmitting SDA=2, SIL=3. One of them has a GTX345R with built-in GPS position source and the other (our RV-7A) has a GTX 45R with GTN 750 external ADS-B position source.
I also looked at an older report with a GPS20A position source connected to a GTX23ES, and it also transmitted SDA=2, SIL=3.
I don't think think there is a problem with you transmitting SDA=3 and the report shows no problem with this, but it is unusual, so not sure if that is affecting whether or not the ground stations provide TIS-B client services to you.
You mention that your 696 and Garmin Pilot displays agree with this FAA report that you are not receiving TIS-B client services. Good to hear since the ground stations send out a list of ICAO addresses that are receiving TIS-B client services every 20 seconds and the GDL39 looks at this list to verify your aircraft address is in the list before telling the displays that your aircraft is receiving these services. At any point that 2 of these updates pass and your aircraft ICAO address is not in the TIS-B client list, the GDL39 tells the displays you are no longer a TIS-B client.
So, lots of words here to say that you "should" have been receiving TIS-B services as long as you were flying high enough on this 36 min. flight to be in radar contact. Was this the case? This is one of the protections in place to make sure there is little chance of someone spoofing the system. No radar contact, no TIS-B client services provided. You say that Madison was vectoring you for traffic, so it sure seems like you should have been in good radar contact, but since this might have been terminal radar approach control, I don't know if this satisfies the radar contact requirements for ADS-B TIS-B services.
In past years it wasn't uncommon to see "holes" in the system when handoffs between ground stations providing TIS-B services would sometimes fail, but the system seems pretty robust these days. On most of our flights the TIS-B Client % is close to 100%.
Thanks,
Steve