1) I can fix that no problem
2) There is an option "Smart Calc" which you can use... Which does exactly what you just said
If you are going to put 750 (Which is unreachable if only burning logs in busy moments) this will cause your problem.
If you will put Smart calc at 500 points while burning logs, it will work exactly as intended and what you need ^^
Once it reaches the point of smart calc it will burn the last logs based on the wintertodt hp% so it will always be able to get rid of all logs without chopping to many.
tl;dr
You just have to put smart calc at 500 points if only burning logs.
750 when also fletching (Gives more loot)
Lemme know if that works for you ^^