Every engine I've had or had dealings with were different. Doesn't matter which plugs, gaps, choke settings or tickler (prime) they all require something different to start easily. They are as different in personality as the members on this forum...and I don't know why. Experimentation seems to be the only answer. Keep trying different things. maybe you'll find that sweet spot.
Low compression can be a culprit. Lots of miles and wear on the rings and cylinder walls can account for that. Maybe your engine is just really well broken in
A year and a half is a lot of riding if it is as you say a 'daily driver'. Any guess as to how many miles or hours you have accrued? Have you changed anything such as octane rating in your gasoline, oil brand or ratio of oil to gas? Did it used to start easily and slowly get harder to fire?