Should I ditch the SPD’s?

I’ve been riding bikes for most of my life including MTB, Trials and now recently road.

All of my previous bikes have had flat pedals and when I ride them (not clipless) and I’ve noticed I have my foot quite far onto the pedal- almost to the point the axel would be under the middle of my foot (way behind the ball of my foot).

After getting a road bike- I took everyone’s advice and bought some Shimano SPD pedals and shoes and have taken all of the advice the internet has to offer with setting up the cleats in the best position.

Despite all of this, I feel like I can’t get into the correct position (at least for me) because I simply can’t get the cleats any further back on the shoe and so I always feel like my feet are too far back on the pedal- the axel is just behind the ball of my foot and I can’t physically move the cleats any further back. I’m a UK size 12- which I’ve no idea if that makes any difference or not.

Am I the only person who has gone through this issue when switching to SPDs and for anyone out there- did you eventually just get used to the new position you have to have your foot?

At this point, I’m considering ditching them as I’m finding it hard to see any potential performance gains with the set up as I simply don’t feel like I’m in the right position and feel like I can’t get as much consistent power through the pedals as I can when I’m riding just flat pedals.

Any advice would be grand.