Hey there!
I really like the Summit. However, I do think that there may be several yoyos on the market better than it for horizontal. When I used kitty string, instead of my normal, rather thick, toxic string in my supernova, it seemed to get through horizontal easier. If I made the switch to a thinner string, could it make horizontal easier?
I don’t think the string thickness changes anything when it comes to horizontal play. However, you may find horizontal easier by varying the length of the string. As far as I’m concerned, I do find horizontal easier with shorter ones.
Ehh it still does horizontal just fine. If you learn to do it in a summit than it can only get easier.