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.

unsigned int nMessageSize = hdr.nMessageSize;
        
        CDataStream& vRecv = msg.vRecv;
        uint256 hash = Hash(vRecv.begin(), vRecv.begin() + nMessageSize);
        unsigned int nChecksum = ReadLE32((unsigned char*)&hash);
        if (nChecksum != hdr.nChecksum)
        {
            LogPrintf("%s(%s, %u bytes): CHECKSUM ERROR nChecksum=%08x hdr.nChecksum=%08x\n", __func__,
               SanitizeString(strCommand), nMessageSize, nChecksum, hdr.nChecksum);
            continue;
        }
        
        bool fRet = false;
        try
        {
            fRet = ProcessMessage(pfrom, strCommand, vRecv, msg.nTime, chainparams);
            boost::this_thread::interruption_point();
        }
        catch (const std::ios_base::failure& e)
        {
            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_MALFORMED, string("error parsing message"));
            if (strstr(e.what(), "end of data"))
            {
                
                LogPrintf("%s(%s, %u bytes): Exception '%s' caught, normally caused by a message being shorter than its stated length\n", __func__, SanitizeString(strCommand), nMessageSize, e.what());
            }
            else if (strstr(e.what(), "size too large"))
            {