Ok I’ll join…
Remember basking is simply a means for your monitor to obtain the necessary heat to thermoregulate. Consider it is in fact a ‘last resort’ after all other potential heat sources have been exhausted and proven inadequate. This is because basking requires physical exposure and therefore danger, naturally sitting out in the open is not the position they want to be in. So extra basking means that something has changed forcing him to use his ‘last resort’ heat source more often. In this case a lot more often. Either there has been an increased need for heat or a previous heat source has been removed.
Only you know if there has been a heat source removed in some way. It sounds like that is not the case. If not…then the question is what could cause the need for more heat, so much so he is compelled to place himself in danger 3 times as much to get it?
Illness? Could be, maybe he is struggling with a parasite or illness that he knows he needs extra heat to deal with.
Eggs? Is she producing eggs and knows she needs the extra heat to be successful? I do not know if this is true but it makes logical sense.
Too much food? Maybe the consistent source of food evenly distributed (one mouse twice a day everyday) has become an issue with his age.
Basking temps too low? Hey there is nothing stating it has to be 130-140. Maybe sometimes 110 is best, or 160. Excessive basking normally indicates low basking temps. Maybe that’s it?
But wait…maybe this is the normal amount of basking? Maybe he has really only lately become comfortable enough to feel safe using it how he has always needed to.
Or a combination of his age and food intake has increased his heat requirements?
I am not sure of this list, I am just thinking ‘out loud’, but you get the idea. There are just too many variables for anyone to accurately speculate on the problem (if there is one). Maybe it is a combination of several things?
The good news is he is eating well. The bad news is that if there really is a problem by the time he stops eating he is most likely a dead-monitor-walkin…so eating is not a good indicator of health; but it does indicate you have some time to figure this out. So change what you can. The easiest by far is his feeding schedule. Change it up. Feed less, feed at different intervals. Probe his enclosure and understand the temp range options you have provided. Next easiest is basking temps. Increase them, increase the basking surface area.
Sorry no specific answers – good luck.
Tom