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.

CAmount nFeesCheck = it->GetModifiedFee();
        int64_t nSigOpCheck = it->GetSigOpCost();
        BOOST_FOREACH(txiter ancestorIt, setAncestors) {
            nSizeCheck += ancestorIt->GetTxSize();
            nFeesCheck += ancestorIt->GetModifiedFee();
            nSigOpCheck += ancestorIt->GetSigOpCost();
        }
        assert(it->GetCountWithAncestors() == nCountCheck);
        assert(it->GetSizeWithAncestors() == nSizeCheck);
        assert(it->GetSigOpCostWithAncestors() == nSigOpCheck);
        assert(it->GetModFeesWithAncestors() == nFeesCheck);
        
        CTxMemPool::setEntries setChildrenCheck;
        auto iter = mapNextTx.lower_bound(COutPoint(it->GetTx().GetHash(), 0));
        int64_t childSizes = 0;
        for (; iter != mapNextTx.end() && iter->first->hash == it->GetTx().GetHash(); ++iter) {
            txiter childit = mapTx.find(iter->second->GetHash());
            assert(childit != mapTx.end()); 
            if (setChildrenCheck.insert(childit).second) {
                childSizes += childit->GetTxSize();
            }
        }
        assert(setChildrenCheck == GetMemPoolChildren(it));
        
        
        assert(it->GetSizeWithDescendants() >= childSizes + it->GetTxSize());
        if (fDependsWait)
            waitingOnDependants.push_back(&(*it));
        else {
            CValidationState state;