Exception Type='OmmInvalidUsageException' when using fixedWidth in view Array

Most likely something primitive, but I wanted to check our understanding:

when creating a view I thought it was a good practice to set the array size as fixed. It looks as if this is triggering an Exception OmmInvalidUsageException.

Please see below is an example of a simple snapshot request using a view array. Is this normal?

AppClient client; OmmConsumer consumer(OmmConsumerConfig().username("user")); 

//Symbols
OmmArray symbolArray;
{
  symbolArray.addAscii("EUR=");
  symbolArray.complete();
}
//Fields
std::vector<thomsonreuters::ema::access::Int64> fields{11,12,13,22,25};
OmmArray viewArray;
//viewArray.fixedWidth(static_cast<thomsonreuters::ema::access::UInt16>(fields.size())); //With this line we are getting 
//"Exception Type='OmmInvalidUsageException', Text='Unsupported fixedWidth encoding in addInt(). Fixed width='5'. '""
//If commented out everything seems to work fine. Is it normal?
for (auto f : fields)
{
  viewArray.addInt(f);
}
viewArray.complete();
ElementList elemList;
elemList.addArray(thomsonreuters::ema::rdm::ENAME_BATCH_ITEM_LIST, symbolArray);
elemList.addUInt(thomsonreuters::ema::rdm::ENAME_VIEW_TYPE, 1);
elemList.addArray(thomsonreuters::ema::rdm::ENAME_VIEW_DATA, viewArray);
elemList.complete();
ReqMsg test;
//Just a snapshot
consumer.registerClient(ReqMsg().serviceName("hEDD").interestAfterRefresh(false).payload(elemList), client);