When the size of the chord symbol music font is increased from the default, it changes the spacing of diagonal chord inversions, moving the bass note away from the diagonal slash.
This chord is at the default 11pt size for both Chord Symbols Font and Chord Symbols Music Text Font:
And this one is the same chord with both fonts bumped up to 16pt:
The white space on each side of the slash increases disproportionately relative to the increase in font size.
Here they are resized to the same font size and overlaid on each other:
It seems to me that the chord symbol shouldn’t change its spacing as it gets bigger.
I know why this is happening: we use a carefully-chosen (and very extensive) set of values to determine the precise kerning for thousands of pairs of symbols when we lay out chord symbols. These values are not always being scaled according to the size of the font you specify. Changing this will be quite a big job, though we’ll certainly look at it in the future.
For the time being I suggest an alternative approach: instead of changing the font style size, try setting the ‘Custom scale’ property for your chord symbols and enlarging them to 150%. This should give you the same visual size, but with the expected kerning between the two parts of the chord symbol and the diagonal slash.