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.

CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck)
{
    AssertLockHeld(cs_main);
    int64_t nTimeStart = GetTimeMicros();
    
    if (!CheckBlock(block, state, chainparams.GetConsensus(), !fJustCheck, !fJustCheck))
        return error("%s: Consensus::CheckBlock: %s", __func__, FormatStateMessage(state));
    
    uint256 hashPrevBlock = pindex->pprev == NULL ? uint256() : pindex->pprev->GetBlockHash();
    assert(hashPrevBlock == view.GetBestBlock());
    
    
    if (block.GetHash() == chainparams.GetConsensus().hashGenesisBlock) {
        if (!fJustCheck)
            view.SetBestBlock(pindex->GetBlockHash());
        return true;
    }
    bool fScriptChecks = true;
    if (fCheckpointsEnabled) {
        CBlockIndex *pindexLastCheckpoint = Checkpoints::GetLastCheckpoint(chainparams.Checkpoints());
        if (pindexLastCheckpoint && pindexLastCheckpoint->GetAncestor(pindex->nHeight) == pindex) {
            
            fScriptChecks = false;