As long as you keep the potatoes "earthed up" until ...say ........... about the beginning of June I don't think they will mind either way. There is no hard and fast rule to growing spuds, they are very robust (but at the same time VERY frost tender!) I would plant mine in the trough rather than the peak but I think it's down to the individual gardener and their previous experiences.
Good luck with them and don't forget, even if they do go wrong it's only a spud after all! ! !

No theres nothing wrong wth extra shoots from any direction ,they should all point straight up anyway eventually, but you can have more control how they grow....if your seed spud is chitting/shooting at both ends as those shoots grow their going to take the shortest route to the surface i.e to the side instead of straight up.......Simply when setting place your spud on its end.....And dont forget to break off any shoots etc on the bottom end...choose the end wth the most chitts or the strongest shoots...... thats your top end.............. Hope ive helped in some way ;)

I've never heard of planting potatoes on the top of the ridge! The whole idea is to keep the growing potatoes covered with soil, how you do this with the seed potato planted on top I'm not sure. I'd carry on doing what you are doing. Digging a trench 15cm deep, setting the seed potatoes out every 25 - 30 cm depending on whether they are early or main crop variety. Back fill the trench with soil and as the leaves start to appear keeping earthing/ridging up until you have a ridge some 15 cm in height. It has always worked for us.

Thank you all. I'll keep my fingers crossed for a good crop!

I'm sure they will be fine CornishS they are very forgiving plants. Make sure they get enough water if it is a dry summer.