Housing Shortage for Pied Flycatchers?

Just returned from a visit to one of my nest box schemes in the Lune valley. Over the past 10 years the number of nesting Pied Flycatchers has increased from one to a high of six pairs in 2016. Today of the 39 nest boxes only four were unoccupied.Of the occupied ones 33 were tits, mainly Blue Tits most of them at the laying stage only two were incubating and two Pied Flycatchers both with only males in attendance.Tit numbers appear to have increased dramatically from just 26 last year to 33 this year and the highest occupation rate to date. It looks as though the tits have survived well over the past mild winter. The high tit occupation rate means there are only 4 empty nest boxes for the later arriving migrant Pied Flycatchers unless they take over the two tit nests which were not yet fully built. Seriously wondering if we should take some more boxes on our next visit. Will check my other Pied Flycatcher wood next week where we have had a peak of 15 in recent years, but there has been plenty of empty nest boxes.
John