in v0.12 https://github.com/bitcoin/bitcoin/pull/7081 (by @luke-jr) was merged adding `-bytespersigop` (with default of 20).

this is preventing simple bare multisig transactions from being accepted into mempool when the size is < 400 bytes.  
eg; https://gist.github.com/rubensayshi/ac4f617207f7a50559e85d61c05800be

from 1-of-7 and onwards they are accepted because the ratio of bytes:sigops is high enough.  
also having 2 or more inputs will work because it again tips the ratio of bytes:sigops over.

the reason mainly being that `GetLegacySigOpCount` calls `GetSigOpCount` with `fAccurate=false`.

It looks like changing `GetLegacySigOpCount` to use `fAccurate=true` would cause side effects in the few other places (`ConnectBlock`, `CheckBlock`, `CreateNewBlock`) and simply adding `fAccurate` as arg to `GetLegacySigOpCount` would affect the value stored in `CTxMemPoolEntry.sigOpCount` which in turn affects a bunch of other things.

{
    if (!tx.IsCoinBase())
    {
        if (!Consensus::CheckTxInputs(tx, state, inputs, GetSpendHeight(inputs)))
            return false;
        if (pvChecks)
            pvChecks->reserve(tx.vin.size());
        
        
        
        
        
        
        
        
        
        if (fScriptChecks) {
            for (unsigned int i = 0; i < tx.vin.size(); i++) {
                const COutPoint &prevout = tx.vin[i].prevout;
                const CCoins* coins = inputs.AccessCoins(prevout.hash);
                assert(coins);
                
                CScriptCheck check(*coins, tx, i, flags, cacheStore);
                if (pvChecks) {
                    pvChecks->push_back(CScriptCheck());