The Collaborative International Dictionary of English v.0.48:

Disproportionable \Dis`pro*por"tion*a*ble\, a.
   Disproportional; unsuitable in form, size, quantity, or
   adaptation; disproportionate; inadequate. --
   Dis`pro*por"tion*a*ble*ness, n. --Hammond. --
   Dis`pro*por"tion*a*bly, adv.
   [1913 Webster]