Polygon and fireblocks expertise

We have a openzepplin hardhat upgradable contract deployed using
https://github.com/OpenZeppelin/openzeppelin-upgrades
with the hardhat plugin. We are trying to deploy this on Polygon Mumbai (testnet) For testing purposes. we plan to use the fireblocks plugin to sign the transaction which needs us to manualy provide gas parameters
via the proxy options.txOverrides

const gasBuffer = 20e8;
proxyOptions.txOverrides =
gasLimit: 4e6, //based on max gas per block
maxFeePerGas: Number(gas.maxFeePerGas) + gasBuffer,
maxPriorityFeePerGas: Number(gas.maxPriorityFeePerGas) + gasBuffer,

the gas values are retrived from the network from the previous block for estimation..
Our transaction is consistently always dropped.
I am looking for some one to guide us with the correct values.
This contract is not public but i suggest you use a generic contract from openzepplin.