In the .HTA file I changed the following line:
If DPI > 120 then
DESIGN_DPI = 160 'dots per inch
'DESIGN_WIDTH = 450 'pixels
'DESIGN_HEIGHT = 365 'pixels
DESIGN_WIDTH = dw 'pixels
DESIGN_HEIGHT = dh 'pixels
to
If DPI > 120 then
DESIGN_DPI = 96 'dots per inch <<---
'DESIGN_WIDTH = 450 'pixels
'DESIGN_HEIGHT = 365 'pixels
DESIGN_WIDTH = dw 'pixels
DESIGN_HEIGHT = dh 'pixels
This seems to have solved my scaling problems. You still need to adjust the Window size from above, reference: Call ReSizeWindow (425,335,500,535) in the code above the ReSizeWindow function. When the DPI is <120 the formula uses the design width and height 500,535 respectively. However when the DPI is >120 it will use the numbers 425,335 and then factor accordingly. To get mine to work I had to reduce those numbers somewhat but it now almost displaces the same as on a system with DPI set to 96.