Identity shows the highest value for very different contigs length

[Sanrrone]

Dears,
Along with greeting you, I found that when I have two contigs of different length, for example: 30.000bp and 3.000bp, they are almost 90% identical. It is ok from the 3000bp perspective but not from 30000bp. I couldn't found a parameter to correct (or select other) value. So, Is there any parameter or flag to adjust the identity values? and would be okay if I correct the values by length ratio? I am looking for an average between them more than the highest value.

thanks you in advance!