From my quick check, about two thirds of Peterborough home fixtures are/were on Fridays - 5 x Sundays / 9 x Fridays from what's left and 1 x Sunday and 2 x Fridays of what's already been run.
Of the 5 Friday clashes I found, all 5 involved BV Elite fixtures.
4 x Friday night home fixtures plus a Friday night away fixture at Somerset,
There are actually 2 x Mondays as well, and which was my total of 7.
But there would be others once fixtures are rearranged and play-off fixtures are arranged.
I don't know the arrangements at the Showground, but maybe speedway can't just swap Fridays to Sundays just like that?