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.

{
    setEntries parentIters = GetMemPoolParents(it);
    
    BOOST_FOREACH(txiter piter, parentIters) {
        UpdateChild(piter, it, add);
    }
    const int64_t updateCount = (add ? 1 : -1);
    const int64_t updateSize = updateCount * it->GetTxSize();
    const CAmount updateFee = updateCount * it->GetModifiedFee();
    BOOST_FOREACH(txiter ancestorIt, setAncestors) {
        mapTx.modify(ancestorIt, update_descendant_state(updateSize, updateFee, updateCount));
    }
}
void CTxMemPool::UpdateEntryForAncestors(txiter it, const setEntries &setAncestors)
{
    int64_t updateCount = setAncestors.size();
    int64_t updateSize = 0;
    CAmount updateFee = 0;
    int64_t updateSigOpsCost = 0;
    BOOST_FOREACH(txiter ancestorIt, setAncestors) {
        updateSize += ancestorIt->GetTxSize();
        updateFee += ancestorIt->GetModifiedFee();
        updateSigOpsCost += ancestorIt->GetSigOpCost();
    }
    mapTx.modify(it, update_ancestor_state(updateSize, updateFee, updateCount, updateSigOpsCost));
}
void CTxMemPool::UpdateChildrenForRemoval(txiter it)
{
    const setEntries &setMemPoolChildren = GetMemPoolChildren(it);
    BOOST_FOREACH(txiter updateIt, setMemPoolChildren) {