I suggest increasing the height of the designer by 15-20%; this will adversely affect 23% of users, but the impact won't be too terrible. The most severe impact will be felt by 8% of users (for whom the screen is already cut off). 

1280 x 720

8% of sessions have 720 or lower

1280 x 800

77% of sessions 800 or greater

1440 x 900

65% of sessions 900 or greater

1280 x 960

53% of sessions 960 or greater

1920 x 1080

38% of sessions 1080 or higher

Attachments:

1280 x 720.png (image/png)
1280 x 800.png (image/png)
1440 x 900.png (image/png)
1280 x 960.png (image/png)
1920 x 1080.png (image/png)