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 (it->second->nHeight < chainActive.Height() - 15) {
            LogPrint("net", "Peer %d sent us a getblocktxn for a block > 15 deep", pfrom->id);
            return true;
        }
        CBlock block;
        assert(ReadBlockFromDisk(block, it->second, chainparams.GetConsensus()));
        BlockTransactions resp(req);
        for (size_t i = 0; i < req.indexes.size(); i++) {
            if (req.indexes[i] >= block.vtx.size()) {
                Misbehaving(pfrom->GetId(), 100);
                LogPrintf("Peer %d sent us a getblocktxn with out-of-bounds tx indices", pfrom->id);
                return true;
            }
            resp.txn[i] = block.vtx[req.indexes[i]];
        }
        pfrom->PushMessageWithFlag(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::BLOCKTXN, resp);
    }
    else if (strCommand == NetMsgType::GETHEADERS)
    {
        CBlockLocator locator;
        uint256 hashStop;
        vRecv >> locator >> hashStop;
        LOCK(cs_main);
        if (IsInitialBlockDownload() && !pfrom->fWhitelisted) {
            LogPrint("net", "Ignoring getheaders from peer=%d because node is in initial block download\n", pfrom->id);
            return true;
        }
        CNodeState *nodestate = State(pfrom->GetId());
        CBlockIndex* pindex = NULL;
        if (locator.IsNull())