I use both the described method and placing the probe inside the enclosure exactly over the middle of the uth. Each has advantages and disadvantages. Interior placement is more accurate for temps if the room changes frequently. Its temps is based off the temp of the ambient air and insulate value of the enclosure. Heavy bottomed enclosures especially do well with this treatment things like tanks or custom enclosures that have higher insulation value like PVCx.

Tubs it is not usually necessary as they transfer heat quickly but they do better in warm rooms too as they lose heat quickly very inefficient heating wise.

hydrofarms suffer from some similar issues that all on offs suffer from to some degree. They have a set point temp but have a on temp and off temp many have a 1 degree under on temp and one degree over off temp. hydrofarms seem to be a bit greater than that, 1 degree over off but on seems to be about 2.5 degrees of so. They 'swing' a bit more. This isn't too bad but all on off style ones tend to swing a bit anyway.

They are at the worst under very narrow conditions but unfortunately the conditions many beginners have. Cool room temps combined with a light weight enclosure like a tub the problem is the tub heats and cools faster than the probe responds. For example the probe may say it is reading 90 the set point but the enclosure as it is heating faster than the probe could be reading 95 the probe shuts off power at 91 when the tub is reading 96 the probe allows the temp to drop the tub cools faster so the probe at 88 but the tub could be at 81. then the cycle starts over. In a warm room 80 or so this cycle is smaller and slower so it isn't a problem. Cool rooms it becomes an issue all on offs have but the hydrofarms is a bit larger. Heavy enclosures like glass tanks heat slowly and cool slowly and will closely match the probes response so the swing is much smaller if any. Make sense?