Perhaps we're talking about different things. If you have 2 textures for example:
Lua Code:
tex1:SetDimensions(100, 100)
tex2:SetAnchor(TOPLEFT, tex1, TOPLEFT, 1, 1)
tex2:SetAnchor(BOTTOMRIGHT, tex1, BOTTOMRIGHT, -1, -1)
1) doesn't mean tex1 is 100x100px; it can be 67x67px, if GetUIGlobalScale() == 0.67
2) doesn't mean there's 1 px border between tex1 and tex2. Could be 1px, 0px or 2px, depending on the scale and alignment.