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 (!boost::filesystem::exists(blocksDir))
    {
        boost::filesystem::create_directories(blocksDir);
        bool linked = false;
        for (unsigned int i = 1; i < 10000; i++) {
            boost::filesystem::path source = GetDataDir() / strprintf("blk%04u.dat", i);
            if (!boost::filesystem::exists(source)) break;
            boost::filesystem::path dest = blocksDir / strprintf("blk%05u.dat", i-1);
            try {
                boost::filesystem::create_hard_link(source, dest);
                LogPrintf("Hardlinked %s -> %s\n", source.string(), dest.string());
                linked = true;
            } catch (const boost::filesystem::filesystem_error& e) {
                
                
                LogPrintf("Error hardlinking blk%04u.dat: %s\n", i, e.what());
                break;
            }
        }
        if (linked)
        {
            fReindex = true;
        }
    }
    
    int64_t nTotalCache = (GetArg("-dbcache", nDefaultDbCache) << 20);
    nTotalCache = std::max(nTotalCache, nMinDbCache << 20); 
    nTotalCache = std::min(nTotalCache, nMaxDbCache << 20); 
    int64_t nBlockTreeDBCache = nTotalCache / 8;
    nBlockTreeDBCache = std::min(nBlockTreeDBCache, (GetBoolArg("-txindex", DEFAULT_TXINDEX) ? nMaxBlockDBAndTxIndexCache : nMaxBlockDBCache) << 20);