My Endless Summer have regrown to almost the size they were last year when I planted them. I think they would have been larger this year IF we had not received a late frost that killed off the new buds that had formed on the old wood. I think at the end of the season this year I will wrap the plants in burlap to offer some additional protection and see if that might help out.
The soil where they are planted is rather sandy although I added about 3" of compost and turned it under at the beginning of spring. They seem to be doing well – but the proof is in the blooms. I’ll be very disappointed if they only produce a couple blooms! I would suggest amending your soil if you can, and see if that helps.