I think the frequency seems good, I have noticed with 3x a week its a good heat loading and seems to help leading up to a trips to Caribbean, HI or FL etc. Maintenance for me seems to help at 1-2x a week. However I go with a more 'hard days hard’ situation, with the ultimate goal of heat stress that triggers high core temp for awhile, so a nice hot sauna at the gym for 20-30min, HR easily gets into the 120-140bpm by the end (resting 47, max 193). So by 15min i am dripping profusely, noticing shortness of breath, by 20-25’ feeling HR ‘issues’ lol and maybe even hints of what I call ‘butteryfly’s all over me’ feeling (like tingly but more fluttery…lol). Before it gets that bad I try to take short 1min recoveries out on pool deck walking, maybe rinse off with warm shower water, then get back in sauna. Idea of getting core at a very warm Temp, for as long as possible, those 1min breaks don’t drop core much at all, before back into the heat.
Timing of mine are pretty random and like you say it doesn’t seem to effect my other training much. I still hit my workouts (i have around 24hr between the evening sauna and next evening hard intervals). Figure my indoor treadmill or indoor trainer rides also supplement the heat training a little cuz no matter what, it gets very warm even on endurance rides (unlike outside).
So my only roast is it seems you are limiting the temperature & stress maybe a bit? IDK - but if you don’t feel a bit faded in the hour/hours after sauna… i’d be hard pressed to say it was a significant message signaler to the body. Ymca sauna is 165 on gauge that has been replaced somewhat recent. Plus was reviewing a airplane parts bonding ‘warming room’ at a production facility recently set to 175° (very monitored)… felt like the sauna, was expecting worse (cuz so close to boiling temperature!). So it seems to track YMCA sauna, so the idea of just 100-110° , not sure how steamy the steam is - compared to people spraying water on the rocks of sauna intermittently.
Maybe push the effort a bit more when it is further from a hard workout?