1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

#codeforces div-3 round

'''for _ in range(int(input())):
    x=input()
    n=len(x)
    if x[0]=="1":
        print(n*(n+1)//2)
    else:
        print((int(x[0])-1)*10+n*(n+1)//2)'''

'''for _ in range(int(input())):
    n=int(input())
    arr=[int(i) for i in input().split()]
    
    ans=0
    last_seen=-1
    for k in range(n):
        if arr[k]!=0:
            if last_seen==-1:
                last_seen=k
            else:
                ans+=k-last_seen-1
                last_seen=k

    print(ans)'''

for _ in range(int(input())):
    n=int(input())
    arr=[int(i) for i in input().split()]

    ans=-1
    t=max(arr)
    for i in range(n):
        if (i>0 and arr[i]>arr[i-1]) or (i<n-1 and arr[i]>arr[i+1]):
            if arr[i]==t:
                ans=i+1
                break

    print(ans)
    
                
    
