I have a different raspberry problem.

We have a patch full width of the allotment, about 1m wide (3 or 4 canes
deep, give or take). The fruit at the east side of the line is weedy and
turns to mush quickly and never grows very big. The fruit at the west of
the line is large and solid and taste much nicer.

Now, we inherited the plants when we took over the plot, so we have no idea
if they are all the same variety or if that's the difference. Other things
I considered are that the sun will be available at different times of day to
the opposite ends. Or that the plots on either side have different amounts
of weed which could possibly be altering the amount of water available.

I'm guessing the most likely thing is that they are different varieties, but
it seems a bit ... haphazard, which is unlike the previous person, who was
very precise about these things.

Have I missed any obvious other potential cause?

I'm considering removing all of the canes on the east side at the end of the
year and replacing them either with different raspberries (new ones or
cuttings from the west side) or with something different.