Coal tit nest site preferences

According to the BTO:

They will use boxes with small entrance holes and there is some evidence to suggest they might prefer nest boxes with a narrow vertical slit to those with a round hole. Their smaller size means that they are often out-competed by the larger relatives when it comes to finding and defending nestboxes. Coal Tits prefer nestboxes mounted on conifers to those mounted on deciduous trees.

Perhaps it was a loaded question.

My local silly begger coal tits (which went AWOL for over 12 months, for reasons I can only suppose) have chosen a gap in a dry-stone wall about 60cm. above ground level. The site also faces west. Lots of beak-fulls of moss going into the hole (there must be a cavity on account of the volumes of moss). The site is also in a place where gardening activity will gear-up in the next weeks.

I can only suppose they may chose lower positioned nest sites to avoid direct competition with other hole nesters. And they also start nesting earlier to remove an element of nest site competition.

I'm suspecting a failed nesting attempt. The nest will overheat (west-facing) as spring progresses, with comensurate cooking of eggs and/or nestlings. There's another hole in another wall (slot dimensions which has been repeatedly used by blue tits, with zero success. It's location is above head height, and with no easy access from above. That is also west-facing. No successful fledgings from that site. That 'hole' is also used by small birds foraging for inverts during the coldest months, hence my reluctance to seal it off.

Just my tuppence worth on bird nest sitings, their positions, opportunities and likely failures.

Had a blue tit nesting in a slot in a steel gatepost. That failed. The nest 'slipped' down the cavity. Possibly due to the operation of the bolt that had to engage with the said slot.

Bird feeders are useful in getting a handle on whether more common species have departed the immediate area.

Pardon my attitudes.