When using the default Tablet settings, iPads usually get a ScreenSize rating of 3 when horizontal and 2 when portrait. I mainly use the ScreenSize for setting to choose from an array of precalculated font sizes that i use throughout the app:
//App.Formulas
f_FontSize4={s20o18: 20, s13o12: 13, s13o11: 13, s12o11: 12, s12o10: 12, s11o10: 11, s11o9p5: 11, s10o9: 10, s9o8: 9};
f_FontSize3={s20o18: 18, s13o12: 12, s13o11: 11, s12o11: 11, s12o10: 10, s11o10: 10, s11o9p5: 9.5, s10o9: 9, s9o8: 8};
f_FontSizes=If(App.ActiveScreen.Size = 4, f_FontSize4, f_FontSize3);
And then I start going through each control on my app pages and giving it an X/Y/Width/Height formula like
App.Width * 0.031 //comment containing the default result when viewed in the editor
However, it may be worthwhile to try only disabling "Lock aspect ratio" so you only have to manage font sizes.