Suggest you run a search as the topic comes up regularly.
At the lower levels, Vmo will be limiting and you may see the IAS limit increase a little as you climb reflecting the EAS. Limit often relates to wing skin structure loading .. occasionally one reads of D-cell destruction in significant exceedances, for instance. At crossover, the Mmo takes over and the IAS reduces with further climb to bring the TAS back in line with local sonic speed.
The actual limiting design case for a given aircraft will not necessarily be obvious.