Unable to get s on mages(Zoe,Syndra)

So,after getting a couple of champions to level 5,specifically Zoe and Syndra,it’s been a hell to get those mastery tokens I long for.I got Zoe to level 6 with really good scores but only s- and for Syndra,I worked super hard to get those s as well but somehow it feels impossible to win tokens for these champs.My usual scores with them vary from 15 to 20kills and 3-5 deaths and cs is always around 150-200,if the game Is long it can reach 250,but still no luck.I don’t think it’s a skill matter but rather something I’m missing.Yesterday i had a game with Syndra,19/1/3,most damage and 200 cs and I only got s,not even s+.I don’t know,getting level 7 on them seems impossible,I don’t know what I should do.Will playing them in any other lane than mid bring different results or something?