Given where you live - try some in the shady garden and see how they do there. And you don't have to lift them, either. Most of them will come back again next season.

I'd say the peat in the mix would be the problem. It can be very hard to rewet once it's reached a certain level of dryness.

You could try adding a soil saturation mix; or some sterile worm castings which act like a fine water-holding soil; or those water crystal thingies; or add some coarse horticultural pumice about 3mm-5mm sizing, not too many fines, to your mix.

Personally, I'd go for the worm casts and the pumice for the aeration, drainage, and water-holding properties.

You might also want to review your basket lining construction to see if another system would give you better results.

I used a thin layer of foam rubber last season, inside a well-holed plastic cover, and it seemed to work. I've also seen a posting by someone who used those 'overnight baby diapers' - with the capacity to hold moisture and slowly release it - as a discreet option in a hanging basket. Carefully smothered by coir or sphagnum - it could work. I don't know anyone who uses them at the moment so I couldn't try it.